Phase III multicenter, randomized, doubleblind, placebo-controlled study. A total of 350 patient will be enrolled and patients will be stratified based on their use of hydoxyurea. Patients will be randomized by a central procedure. Once eligibility has been determined & informed consent has been obtained, patients will be randomized by a central procedure. Patients will be stratified based on their use of hydroxyurea & sickle cell genotype (SS,SC,SB+thal,SB thal) will be randomly assigned 1:1 to placebo or FLOCOR. The treatment phase will last 48 hours during which the patients will receive the study drug or placebo. At the same time patients will receive hydration and analygesia as required by their condition. Once the treatment phase has been completed patients will be monitored for 5 days or until the crisis has resolved, whichever is shorter. Follow up evaluations will be performed 7-14 days and 28-35 days after the initiation of treatment.